The present invention relates particularly to fastener mechanisms such as bolts and screws.
For ease of general reference both bolts and screws are understood to include a head and a threaded shaft. Bolts tend to differ from screws in that bolts tend to have an even cross-section throughout the shaft (excluding the effect of the threads) whereas screws tend to be tapered to a point at the end of the shaft distal to the head. As can be appreciated there are many thousands of variations on bolts and screws to which the principles of the present invention can be applied.
It should be appreciated that the fastener industry is internationally estimated at being worth US $40 billion per annum.
One of the major disadvantages with current bolts is that it is estimated that approximately 50% of mechanical failures occur as a consequence of nuts and bolts shaking loose.
An extreme example of such failures is the crash of a Concorde at Charles De Gaulle Airport in Paris. This occurred because a small metal strip fell off a DC10 plane onto the runway.
There have been numerous attempts and many patents filed which discuss the efforts of parties around the world to invent a fastening mechanism in the form of a bolt that strongly secures elements together but does not shake loose with vibration.
One example of a product developed to decrease the effect of vibration on screws and bolts is the Nylok product, Blue® Patch.
This product includes a thin patch which is spray bonded onto the threads of a fastener. The patch then acts as a self locking element.
The principle behind the patches is that when mating threads are engaged the self locking patch element is compressed and a counterforce is created to establish a stronger metal to metal contact, and thus provide increased resistance to vibration and loosening.
This product however has a number of significant disadvantages, these include the following:
One disadvantage is that although the patch is meant to be ‘permanently’ spray bonded onto the threads of a fastener, the patch may become separated from or tatty with repeated use. The patch once applied to the thread covers the entire thread in the area applied, including the protrusions and depressions of the thread. The patch is highly prone to permanent deformation or deterioration in use. This is especially the case when mis-threading occurs or when bolts or screws are tightly fitted into their opposite member a number of times. Any separation of the patch decreases the effect of the patch, and may result in uneven action or failure of the patch.
Where a part is disassembled for inspection or maintenance, it is advantageous if the fastener used does not deteriorate in anti-vibration efficacy with each use, and a Blue® Patch is prone to do so.
A further significant disadvantage of these patches is that at high or sustained vibration levels the patch effectiveness may be decreased. This may be due to the thinness of the patch material, detachment of the patch under these conditions, or lack of resilience in the patch material.
These problems significantly reduce the reliability and reusability of this product.
The same technology as that employed in the Nylok® Blue® Patch has also been applied to the interior thread of nuts which are then fitted over bolts.
The same problems as discussed above apply in this situation.
Long-Lok Fasteners Corporation is another company which provide patches for fasteners such as their product Poly-Lok®. These also have the same disadvantages as discussed above.
Long-Lok Fasteners Corporation also has a product which is sold under the name of Long-Lok®. This is a bolt which has a strip cut into its longitudinal axis. The cut is then filed with a vibration resistant material such as Nylon or Kel-F®.
This material is highly subject to deterioration as it is “cut” into by the complementary thread into which the bolt is done up or undone from. Repeated use of the bolt can therefore significantly decrease the effect of the material to dampen the effect of vibration which is required to prevent the bolt from loosening.
One significant disadvantage with this product is that the Nylon or Kel-F® material is placed under considerable forces as the bolt is done up, or a nut is placed on same. This can significantly weaken the material and decrease the effectiveness and reusability of the product.
A further disadvantage is that due to the material being positioned along a longitudinal axis of the bolt, the material may only be effective in decreasing the effect of vibration when the vibration is from a particular angle, for example when the vibration is in the same plane as the material is positioned.
The position of the material along the longitudinal axis of the thread leads to non-uniform deformation along the length of the material. For example, a protrusion or a depression on the complementary thread to the bolt will lead to differing deformation on adjacent portions of the material. This non-uniform deformation is unreliable, and decreases usability.
Other disadvantages, discussed above in relation to a patch sprayed onto the threads also apply to this product.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.